1. Field of the Invention
Some preferred embodiments of the present invention relate to an electric fader drive unit that drives an electric fader of a light dimmer, an audio mixer, or the like.
2. Description of the Related Art
A light dimmer used in a stage or a studio is capable of controlling the brightness of lighting by adjustment of the position of a fader of the light dimmer. Similarly, an audio mixer used in a stage or a studio is capable of adjusting volume, a tone, or the like, by adjustment of the position of a fader of the audio mixer.
Some light dimmers or some audio mixers include an electric fader. The electric fader includes a fader, a motor, and a belt that moves the fader. An electric fader drive unit, when receiving an indication of a target position, drives the electric fader and moves the fader to the target position.
The electric fader drive unit is capable of storing a fader position determined in the past and reproducing the brightness of the lighting determined in the past or the volume or the like determined in the past, by reading out a stored fader position as the target position.
The electric fader is required to move to the target position smoothly and accurately. In order to stop the electric fader at the target position smoothly and accurately, the speed of operation needs to be a comparatively low speed. In order to make the speed of operation into such a comparatively low speed, the electric fader needs to be driven with comparatively low drive power. However, the electric fader has an individual difference or a change over the years. Accordingly, when driven with low drive power, the electric fader may not obtain a sufficient drive power and may stop before reaching the target position. In order to prevent the influence of such an individual difference and a change over the years, it is necessary to set the drive power to be comparatively high. However, when driven with comparatively high drive power, the electric fader may stop at a position beyond the target position (overshoot may occur).
In view of the foregoing, an electric fader drive unit disclosed in Patent Literature 1 (Japanese Patent No. 2684808), for example, performs control of significantly reducing drive power if an electric fader in a current position approaches a target position. In addition, an electric fader drive unit disclosed in Patent Literature 2 (Japanese Patent No. 3775368) controls drive power so that the movement speed of a fader does not exceed a predetermined movement speed.
However, such conventional electric fader drive units have generated sound while driving the electric fader. Such sound is generated because a belt is bent, for example. The belt as a component of a drive system needs to be bent. If a large drive power is suddenly applied to the belt, the state of the belt is suddenly changed from a bent state to a tension applied state, which generates the sound.
The sound generated by the electric fader drive unit may become a noise that has a bad influence on the surrounding environment. For example, since the sound can be easily heard in a quiet studio, the sound generated by the electric fader drive unit is perceived as a noise.